Iron-mediated synthesis of C.I. pigment violet 23 and triphenodioxazine -based derivatives: A novel and efficient approach

A novel and efficient method for the synthesis of Pigment Violet 23 and triphenodioxazine (TPDO)-based derivatives has been developed through safe, low-cost iron-mediated and green air-assisted oxidative cyclization. Using this method, Pigment Violet 23 and a variety of substituted TPDO derivatives were afforded in good to excellent yields. The characteristic UV–vis absorption wavelength of our prepared C.I. Pigment Violet 23 (λ: 546, 588 nm) in 1,4- dioxane was almost the same as that of commercial C.I. Pigment Violet 23 (λ: 542, 589 nm), and its derivatives 6b∼6f exhibited two intense sharp peaks in the range of 500–650 nm. Also, intense sharp peaks of derivatives 6a, 6g∼6i, 6j, 6m, 6q were in the range of 450–550 nm. In addition, two isomers 6g-1, 6g-2 generated from the 3-tert-butyl-substituted compound 5g were separated and validated, which could further confirm that the prepared C.I. Pigment Violet 23 was the mixture of 6b-1, 6b-2 and 6b-3.